Re: [PATCH] cpufreq/amd-pstate: Use sysfs_match_string() for epp

Gautham R. Shenoy
2025-10-09T04:32:45Z

Hello Mario,

On Wed, Sep 24, 2025 at 12:50:16PM -0500, Mario Limonciello (AMD) wrote:
> Rather than scanning the buffer and manually matching the string
> use the sysfs macros.

This is a nice optimization.

While at it, would it be possible to get rid of the "NULL" entry from
the energy_perf_strings array ?

Something like the following in addition to the change in your patch?

--------------x8---------------------------x8----------------------------
diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
index 34835681be92..bd022dd21a4a 100644
--- a/drivers/cpufreq/amd-pstate.c
+++ b/drivers/cpufreq/amd-pstate.c
@@ -117,8 +117,7 @@ static const char * const energy_perf_strings[] = {
[EPP_INDEX_PERFORMANCE] = "performance",
[EPP_INDEX_BALANCE_PERFORMANCE] = "balance_performance",
[EPP_INDEX_BALANCE_POWERSAVE] = "balance_power",
- [EPP_INDEX_POWERSAVE] = "power",
- NULL
+ [EPP_INDEX_POWERSAVE] = "power"
};

static unsigned int epp_values[] = {
@@ -1180,7 +1179,7 @@ static ssize_t show_energy_performance_available_preferences(
return sysfs_emit_at(buf, offset, "%s\n",
energy_perf_strings[EPP_INDEX_PERFORMANCE]);

- while (energy_perf_strings[i] != NULL)
+ for (i = 0; i < ARRAY_SIZE(energy_perf_strings); i++)
offset += sysfs_emit_at(buf, offset, "%s ", energy_perf_strings[i++]);

offset += sysfs_emit_at(buf, offset, "\n");
--------------x8---------------------------x8----------------------------

>
> Signed-off-by: Mario Limonciello (AMD) <superm1@kernel.org>
> ---
> drivers/cpufreq/amd-pstate.c | 7 +------
> 1 file changed, 1 insertion(+), 6 deletions(-)
>
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index ba2adea03db1..b8af6cad9e2c 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -1157,15 +1157,10 @@ static ssize_t store_energy_performance_preference(
> struct cpufreq_policy *policy, const char *buf, size_t count)
> {
> struct amd_cpudata *cpudata = policy->driver_data;
> - char str_preference[21];
> ssize_t ret;
> u8 epp;
>
> - ret = sscanf(buf, "%20s", str_preference);
> - if (ret != 1)
> - return -EINVAL;
> -
> - ret = match_string(energy_perf_strings, -1, str_preference);
> + ret = sysfs_match_string(energy_perf_strings, buf);
> if (ret < 0)
> return -EINVAL;
>
> --
> 2.51.0
>

--
Thanks and Regards
gautham.